The host of that video is Andrew Millison, who is deeply involved in permaculture design, and has a lecture series with the University of Oregon. Permaculture design is a fairly involved design process, so if you think this video is about "just plop down a pond!", you missed a lot of the main ideas.
For context:
- Millison's lecture on different pond designs: https://www.youtube.com/watch?v=AadLCOqalFk
- Related is the design for slope: https://www.youtube.com/watch?v=McopD04XP3s
- Keep in mind, you actually start with site analysis: https://www.youtube.com/watch?v=-XNiacRhzuM (starting from the global and coming down to the local, and then moving on to sector, zone, and slope analysis, all _before_ figuring out the placement of water harvesting structures)
Instead of thinking about these ponds as "ponds", these are really one form of water harvesting structures in permaculture design. And there are many kinds of water harvesting structures, each with its own tradeoffs, and how the work holistically together with other considerations such as microclimates (or even creating microclimates), sun, rain, wind patterns, and how they work with the inhabitants (both human and otherwise).
These ponds are not created for just irrigation. It's more sophisticated than that. The ones in the video are created as percolation ponds, and intended to recharge ground water. The idea is to slow water down and circulate it within the site before letting it flow on. The water held in percolation ponds are intended to be leaky. By redirecting flow laterally, the water is distributed across a larger area. It isn't just about water, but also about regenerating the soil in such a way that it is able to absorb and retain more water and nutrients, while cooling and regulating the local area, forming a microclimate. Counter-intuitively, more water becomes bio-available downstream rather than less.
Beavers used to do this across North America, and many of the permaculture patterns for managing water has analogs to what the beavers naturally do.
It's the modern irrigation practices which maximizes water usage without really considering how soil health plays a huge role in retaining water makes it less efficient in water usage. So we end up with water wars and the inability to grow crops during drought conditions. We fight over water rights when it is our land and water management practices that causes much of the problems in the first place.
Millison has a video series about what people in India are doing to regenerate wastelands that receive very little water fall. The general problem are the same -- monsoon season water running through the landscape too fast, eroding soil, which means less crops, and setting off a pattern of rural migrations. When villages are able to slow down the water flow, they were able to grow more crops. Many of the water harvesting structures built at the higher elevation slow water enough down where the downstream areas became more abundant.